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Galileo satellites experiencing problems with the onboard clocks

Thu 19th January 2017

The onboard atomic clocks that drive the satellite-navigation signals on the new Europe's Galileo network have been failing at an alarming rate.

Across the 18 satellites now in orbit, nine clocks have stopped operating.

Galileo was declared up and running in December and here at GPS training we flagged it up in early January once we heard back from Garmin regarding to compatibility with their outdoor GPS units.

With a number of the current fully functioning satellites in orbit not being at a number that makes it fully function able and with the suggestions that future launches may be suspended until the atomic clock problem can be resolved it may again delay the date the complete system will be up and running for users.

Each Galileo satellite carries two rubidium and two hydrogen clocks. The multiple installation enables a satellite to keep working after an initial failure. All 18 spacecraft currently in space continue to operate, but one of them is now down to just two clocks.

A statement issued by the agency late on Wednesday gave additional details.

It appears the rubidium failures "all seem to have a consistent signature, linked to probable short circuits, and possibly a particular test procedure performed on the ground".

The maser clock failures are said to be better understood, with two likely causes, the second of which has caused most grief.

The Esa statement said this second scenario was "related to the fact that when some healthy [hydrogen maser] clocks are turned off for long periods, they do not restart due to a change in clock characteristics".

Actions are being taken to try to prevent further problems. These involve changing the way clocks are operated in orbit. Clocks about to fly are also likely to be refurbished, and future devices yet to be made will have design changes, the agency says.

Esa is hopeful it can still launch the next four satellites in the constellation before the end of the year.

Precise timing is at the core of all satellite-navigation systems.

Atomic clocks generate the time code that is continuously transmitted to users on the ground to help them fix a position.

A fully operational Galileo system is regarded as a constellation of 24, split across three orbital planes in the sky. But spares are required also, and with one very early satellite in the constellation already considered very close to complete failure - for different reasons - there needs to be near-continuous production of spacecraft.

The four latest satellites went up as a quartet in November; more are set to follow later this year.

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